Vessel for measuring oxygen content of a molten metal



Sept 24, 1968 ncl-1| TAJIRI TAL 3,403,090.

VESSEL FOR MEASURING OXYGEN CONTENT OF A MOLTEN METAL ncl-u TAJIRI ET AL 2 Sheets-Sheet 2 F I G 6 FI G'. 7

JA/VE/VTOHS, I ich I Siro QBY Sept. 24, i968 VESSEL FOR MEASURING OXYGEN CONTENT OF A MOLTEN METAL Filed May 4, 1965 Flexs United States Patent O s claims. (cl 204-195) This invention relates to la vessel for continuously measuring the oxygen content in a molten metal.

As a method for measuring electrochemically the oxygen content in a molten metal, a method has been known wherein a refractory material is used as an intermediate electrolyte together with Ia standard electrode material for giving a constant oxygen potential to form an electrolytic cell consisting of molten metal, for instance, molten steel-intermediate electroltye-standard electrode and the oxygen content in the molten steel is calculated from the electrtomotive force of the electrolytic cell.

The present invention is, in particular, concerned with a vessel for detecting continuously the oxygen potential in a molten metal during an industrial smelting process or others based on the above-mentioned principle.

That is, an object of this invention is to provide a molten metal vessel, in the wall of which a standard electrode is inlaid for continuously measuring the oxygen potential of a molten metal in the vessel. This and other objects of this invention will become clear from the following description and the accompanying drawings, in which:

FIG. l is a schematic cross-sectional view showing an embodiment of this invention wherein a standard electrode and metallic electrode are inlaid in the bottom of the melting furnace in order to measure the oxygen potential in the molten metal,

FIG. 2 is a graph showing the relation between the electromtive force and the analytic value of oxygen in the steel and ythat between the electromotive force measured. by using the melting furnace shown in FIG. 1,

FIG. 3 is a schematic cross-sectional view showing another embodiment of-this invention, n FIGS. 4 and 6 are a schematic cross-sectional view showing an embodiment of applying the system of inlaying the standard electrode shown in FIG. 3 to a molten metal vessel of an industrial scale, respectively, in which FIG. 4 relates to a position of inlaying the detecting means into a 8O ton ladle and FIG. 6 into a 130 ton converter, y

FIGS. and 7 are schematic views showing development of the inlaying states shown in FIGS. 4 yand 6, respectively.

According to the present invention relating to a molten metal vessel for measuring the oxygen potential in the molten metal a standard electrode alone or together with a metallic electrode are inlaid in the side wall or the bot- Y tom wall of the vessel through the wall thereof, whereby the system may be protected from erosion and contamination caused by slags, and various operations in the vessel may be carried out without being infected, which make possible the stable and continuous measurement of the oxygen potential in the molten metal for a long period of time.

Further, it is -also within the scope of the present invention to measure an oxygen potential continuously and always preciselyfor a long period of time by providing an arrangement in which a plurality of the standard electrodes Vis inlaid in the wall of the vessel at various distances from the inner surface of the vessel wall to the tip of each standard electrode, and there is installed a ice switch which is switched over in turns from one electrode to a new one to be exposed by erosion by melting of the vessel wall.

The invention will further be explained referring the accompanying drawings.

FIG. 1 is a schematic view of a melting furnace as an embodiment of the vessel according to the present invention, wherein the detecting means of the present invention are inlaid in the bottom wall of a high frequency induction furnace having a melting capacity of 10 kg. whereby the oxygen potential of a molten steel in the furnace can be continuously measured.

As shown in FIG. l, 1 is an induction coil for heating, 2 is a Crucible made of electrocast magnesia. 3 is a refractory material layer for heat insulating said crucible and for preventing leakage of molten metal. The standard electrode consists of a refractory shell 4 made of sintered magnesia which is to serve as an intermediate electrolyte, said refractory shell being filled with powered standard electrode material 5, which is to give a constant oxygen potential to the standard electrode, and with a conducting electrode 6, that is, a material which can be a conductive body without disturbing the constant oxygen potential of the standard electrode, said standard electrode being so inlaid in the vessel wall that the one end of said electrode is exposed to the inner surface of the Crucible through said Crucible wall 2 and the other end thereof is connected with a balance-type electron tube automatic recorder 9. 7 is a refractory plug for preventing cutting by melting of a mild steel rod 8 as a metallic electrode and for securing electric and thermal insulation.

As clearly understood from FIG. 1 an advantage of this invention resides in the points that by equipping the detecting means in the bottom of the furnace, the detecing elecrodes can be protected from erosion by molten slag and violent agitating motion of the molten metal, and that the working property of the furnace is much better as compared with a conventional process in which the electrodes are immersed from above in the bath.

In the experiment shown in the example of this nvention the standard electrode consisting of the refractory shell 4 of intermediate electrolyte, the standard electrode material 5 and the conducting electrode material 6 is prepared by using sintered magnesia for said refractory shell 4, powered graphite for said material 5, and graphite rod for said material `6. But other combinations of electrode materials of various kinds are also applicable. For instance, as material for the intermediate electrolyte shell 4 an oxide such as magnesia, alumina, silica, zirconia or -beryllia may be adopted. For powdered material 5 a reducing a non-oxidizing material such as graphite or silicon carbide may be used, and for the electrode material 6, a material having high-temperature resistance and which is not denatured in a reducing atmosphere is required, such as graphite, silicon carbide, tungsten, or other metal wire of high melting point.

In the following the process of measuring the oxygen potential in the molten steel while charging the vessel of the present invention with the same will be explained.

7 kg. of electrolytic iron and an excessive amount of carbon -are charged in a melting furnace shown in FIG. l and melted by high frequency induction heating. When the charge is melted the recorder 9 shows immediately the oxygen potential of the molten metal, but since the bath temperature in this period is unstable, the recorded value is not reliable. Hence, the bath temperature should be stably maintained yat 1,550 C. as quickly as possible. After maintaining the constant temperature, the recorder is sta-rted in operation to record the electromotive force. Then, the bath is subjected to decarb-urization by lblowing an oxygen yblast onto the molten metal and the increase in the oxygen potential during decarburization is continuously recorded on the recorder. Further, during the abovementioned blowing, specimens for analyzing oxygen and carbon are taken out every definite period of time. The relation between the thus obtained electromotive force and the analyzed value of oxygen (O) in the steel and that between the electromotive force and the analyzed value of carbon (C) in the steel are shown in FIG. 2.

As evidently seen from FIG. 2 there are very high relations between the thus measured electromotive force and the analyzed values of oxygen and carbon in the steel.

Further tests in cases where sintered alumina or silica was used as the material for the intermediate electrolyte, silicon carbide as the powdered material 5, and a tungsten wire or rod as the electrode -material 6 showed that stable records could be obtained in any case. In conclusion, it has been confirmed that the conditions required for effecting the method of inlaying the standard electrode in the bottom of the furnace as adopted in the example of the present invention are to use an oxide refractory material, such as alumina, magnesia, silica, zirconia, beryllia, or thoria as the intermediate electrolyte, a lowoxygen potential material, such as graphite or silicon carbide as the powdered material for the standard electrode for giving a constant oxygen potential, and a high melting point non-oxidizing material which is not denatured in a reducing atmosphere, such as graphite, tungsten or nickel as the conductor material.

Next, another embodiment of the present invention, though carried out also on a laboratory scale as in the foregoing embodiment, will be explained, in which a standard electrode having a comparatively high oxygen potential is used.

The schematic cross-sectional view of the melting furnace used in the present example is shown in FIG. 3. The materials and purposes of the numerals 1, 2, and 3 in FIG. 3 are the same as in the aforementioned embodiment. but the electrocast magnesia plus 4 is used simultaneously as the intermediate electrolyte and the standard electrode material, and the conductor 5 is made of a platinum electrode. The numeral 6 denotes a refractory plug for preventing cutting by melting of a mild steel rod as the metallic electrode and securing electric and thermal insulating, 7 is a metallic electrode of a mild steel wire material and 8 is a balance-type electron tube automatic recorder.

The melting furnace of this embodiment has the advantage that 'since the standard electrode is constructed by a refractory plug, if the erosion of the furnace bottom proceeds to melt the tip of the standard electrode whereby the electrodes lose the function as electrolytic cell, there are no troubles of molten metal leakage owing to the sufiicient durability of the refractory plug as the structural material for the furnace. Therefore, even if in this embodiment such a melting furnace as a converter would be used, in which a remarkable loss by melting of the furnace material is caused by the operation of the furnace, the measurement of the oxygen potential of the molted steel may be continuously carried out for a long period of time by varying the distance from the inner surface of the furace wall to the tip of the standard electrode in inlaying 'several electrodes of refractory plugs in the wall of the furnace bottom. For the standard electrode material used in this embodiment, magnesia, alumina, zirconia, silica, and 4beryllia are suitable for the refractory plug and a high melting point material having a high chemical stability, such as platinum, platinum-rhodium, nickel, etc., is suitable for the conductor material.

From these 'standpoints, the invention will not be described with reference to FIGS. 4 to 7 relating to cases where the electrode structure of this invention is applied to a molten metal vessel of an industrial scale.

That is, FIG. 4 is a schematic cross-sectional view of an 80 ton ladle showing the state where the above-mentioned detecting means are equipped in the wall of said ladle and FIG. 6 is another schematic cross-sectional view of a 130 ton convertor showing the state Where the 'similar detecting means are equipped in the wall of said convertor. The developments of these are shown in FIG. 5 and FIG. 7, respectively. As the same symbol designates each part of the same construction shown in each of these figures, a detailed explanation will be given in gross to each of the constructions.

In the figures, (A) denotes the position where the detecting means are mounted in a wall and (B) denotes the line showing the limit where the inside wall of the vessel is eroded and the numbers shown in FIG. 4 and FIG. 6 show thickness of the inside wall that may be eroded out. In FIGS. 5 and 7, (a) designates the molten metal side, (b) a refractory layer lining, (c) iron shield, (d) refractory cement, (e) molten erosion line, (f) a switch, an-d (g) an electron tube recorder. Further, (D) in FIGS. 5 and 7 denotes a refractory plug, (F) a mild steel rod sealed in a refractory plug as a detecting means and (B1), (B2) (B5) show a plurality of standard electrodes inlaid in the wall of the furnace at various suitable depths such that even if the tips of the individual standard electrode is eroded by melting, the oxygen potential in the molten steel in the vessel can be continuously and stably measured for a long period of time. If such erosion occu-rs to the standard electrode, e.g., denoted by (B1) which is placed in the bottom wall of the vessel at a comparatively shallow depth from the molten metal, the switch (f) is shifted to the next standard electrode denoted by (B2) and so on, whereby the electromotive force can be measured stably. In other words, according to the present invention the electromotive force may be measured by the arrangement in which a plurality of standard electrodes (B1, B2' B3) is inlaid in the wall of the vessel in advance at various distances from the inner surface of the vessel wall to the tip of each standard electrode, and there is installed a switch which is switched over from B1 to B2 and so on in turns in accordance with the exposure of the tip surface of the electrode when erosion by melting of the vessel wall proceeds.

What we claim is:

1. A molten metal vessel for measuring the oxygen content in a molten metal in the vessel, comprising at least one standard electrode consisting of a refractory shell of intermediate electrolyte of an oxide selected from the group consisting of magnesia, zirconia, alumina, silica, beryllia and thoria, said shell being filled with powdered material of low oxygen potential selected from the group consisting of graphite and silicon carbide and a conducting body material selected from the group consisting of graphite, tungsten and nickel, said standard electrode being so inlaid in the vessel wall that one end of said standard electrode is exposed to the inner surface of the vessel through the vessel wall and the other end thereof is connected with a balance-type electron tube automatic recorder.

2. A molten metal vessel according to the claim 1, in which the standard electrode is inlaid together Iwith a metallic electrode made of a substance selected from the group consisting of iron, tungsten and nickel in the vessel wall.

3. A molten metal vessel according to claim 1, in which -a plurality of the standard electrodes is inlaid in the vessel wall at various distances from the inner surface of the vessel wall to the tip of each standard electrode, and a switch is adapted to be switched over in turn from one standard electrode to the other in accordance with erosion by melting of the vessel wall.

4. A molten metal vessel for measuring the oxygen content in a molten metal in the vessel, comprising a standard electrode consisting of an intermediate electrolyte shell of an oxide selected from the group consisting of magnesia, zirconia, alumina, silica, beryllia and thoria, a conducting body made of a substance selected from the group consisting of platinum, platinumrhodium, silicon carbide and graphite being inlaid in 5- A molten metal vessel according to claim 4, in 5 which the standard electrode is inlaid together with a metallic electrode made of a substance selected from the group consisting of iron, tungsten Iand nickel in the vessel wall.

References Cited UNITED STATES PATENTS 6/ 1964 Tragert et al. 136-86 9/1964 Postal 136-153 6 3,216,911 11/1965 Kronenberg 204-1.1 3,297,551 1/ 1967 Alcock 204-195 OTHER REFERENCES Steinmetz: UNC Project 2176, Contract At (3G-1)- 2877 for the USAEC.

Kiukkola et al.: J, of Electrochemical Soc., vol. 104,

No. 6, June 1957, pp. 379-385.

Horsley: ABRE-R 3037, UK Atomic Energy Authority.

HOWARD S. WILLIAMS, Primary Examiner.

T. TUNG, Assistant Examiner. 

1. A MOLTEN METAL VESSEL FOR MEASURING THE OXYGEN CONTENT IN A MOLTEN METAL IN THE VESSEL, COMPRISING AT LEAST ONE STANDARD ELECTRODE CONSISTING OF A REFRACTORY SHELL OF INTERMEDIATE ELECTROLYTE OF AN OXIDE SELECTED FROM THE GROUP CONSISTING OF MAGNESIA, ZIRCONIA, ALUMINA, SILICA, BERYLLIA AND THORIA, SAID SHELL BEING FILLED WITH POWDERED MATERIAL OF LOW OXYGEN POTENTIAL SELECTED FROM THE GROUP CONSISTING OF GRAPHITE AND SILICON CARBIDE AND A CONDUCTING BODY MATERIAL SELECTED FROM THE GROUP CONSISTING OF GRAPHITE, TUNGSTEN AND NICKEL, SAID STANDARD ELECTRODE BEING SO INLAID IN THE VESSEL WALL THAT ONE END OF SAID STANDARD ELECTRODE IS EXPOSED TO THE INNER SURFACE OF THE VESSEL THROUGH THE VESSEL WALL AND THE OTHER END THEREOF IS CONNECTED WITH A BALANCE-TYPE ELECTRON TUBE AUTOMATIC RECORDER. 